Haemodynamic responses to dehydration in the resting and exercising human leg

Dehydration and hyperthermia reduces leg blood flow (LBF), cardiac output (\( \dot{Q} \)) and arterial pressure during whole-body exercise. It is unknown whether the reductions in blood flow are associated with dehydration-induced alterations in arterial blood oxygen content (C _aO₂) and O₂-dependent signalling. This study investigated the impact of dehydration and concomitant alterations in C _aO₂ upon LBF and \( \dot{Q} \). Haemodynamics, arterial and femoral venous blood parameters and plasma [ATP] were measured at rest and during one-legged knee-extensor exercise in 7 males in four conditions: (1) control, (2) mild dehydration, (3) moderate dehydration, and (4) rehydration. Relative to control, C _aO₂ and LBF increased with dehydration at rest and during exercise (C _aO₂: from 199 ± 1 to 208 ± 2, and 202 ± 2 to 210 ± 2 ml L⁻¹ and LBF: from 0.38 ± 0.04 to 0.77 ± 0.09, and 1.64 ± 0.09 to 1.88 ± 0.1 L min⁻¹, respectively). Similarly, \( \dot{Q} \) was unchanged or increased with dehydration at rest and during exercise, whereas arterial and leg perfusion pressures declined. Following rehydration, C _aO₂ declined (to 193 ± 2 mL L⁻¹) but LBF remained elevated. Alterations in LBF were unrelated to C _aO₂ (r ² = 0.13–0.27, P = 0.48–0.64) and plasma [ATP]. These findings suggest dehydration and concomitant alterations in C _aO₂ do not compromise LBF despite reductions in plasma [ATP]. While an additive or synergistic effect cannot be excluded, reductions in LBF during exercise with dehydration may not necessarily be associated with alterations in C _aO₂ and/or intravascular [ATP].